The present invention relates to a virtual studio and in particular to position sensing system for such a studio.
In virtual studio systems a chroma-key background is provided in front of which an actor stands. In the TV picture seen by the viewer the chroma-key background is replaced by a virtual scene. Such a system is described in PCT Patent Application No. WO95/30312 to the present applicant.
In the above known system the position of the camera is calculable by using a coded pattern on the chroma-key background. This enables the position of the camera, as well as its orientation and the lens zoom, to be continuously calculated and thereby the perspective of the virtual 3D set can be adjusted correctly to suit the camera position.
This works perfectly for cameras which have a fixed focus and zoom or a fixed position but problems can be encountered in situations where the cameraman is free to simultaneously change the camera position and the lens zoom. For example, when the camera""s optical axis is perpendicular (or almost perpendicular) to the patterned wall, the changes in the captured pattern due to zooming of the lens or to changing the distance of the camera from the wall are identical (or almost identical) and the system cannot extract the correct solution from the captured pattern.
The system of WO95/30312 also works well providing that the background panel is a patterned chroma-key panel. However the system does not work where a normal studio or stage set with real background is used.
Thus, if it is desired to position a virtual 3D object in a normal stage set this cannot be done except for a static camera because the position of the camera relative to the stage set cannot be calculated as the camera moves.
It is a first object of the present invention to enable the position of a camera to be calculated in a normal stage set in which the stage set may comprise a real background.
It is a further object to enable virtual 3D objects to be positioned in a normal stage set.
The present invention provides a further object to enable actors who represent foreground objects to wear colours which would otherwise clash with a normal chroma-key background panel. Thus, assuming that a chroma-key background panel in an arrangement such as in WO95/30312 is a combination of light and dark blue patterns in such a prior arrangement the actors cannot wear blue which is extremely restrictive.
In the present invention the actors can wear any colour and the background real set can be any colour.
The background real set does not have to be flat.
In accordance with the present invention a plurality of LED""s are positioned in a real stage set, the LED""s forming a pattern which is known from an initial measurement of the position of each LED.
The LED""s preferably operate in the non-visible spectrum to be thereby non detectable by a normal video camera.
The LED outputs are detected by a detector camera mounted on a TV camera, the pattern formed by the LED""s being utilised to compute the position of the TV camera.
The present invention therefore provides a camera positioning system for a virtual studio, said system comprising a camera, an auxiliary detection device mounted on said camera, a plurality of light emitting devices (LED""s) mounted in known positions to form a defined array and including electronic detection means connected to said detection device, said detection means comprising position sensing analysis means for analysing the perspective of the defined array, as detected by said detection device, to provide a positional read out defining the position of said camera relative to the LED array.
Preferably the camera is a television camera.
Preferably the detector device comprises a detector camera which is preferable boresighted to be aligned with the TV camera.
In a preferred embodiment the LED""s are infra-red operating at a frequency outside the frequency range of the TV camera.
Preferably each LED emits light in a coded form, thereby enabling each light source to be individually identifiable.
Preferably the LED""s are fixed to or positioned in a fixed relationship relative to a real scene.
Preferably the LED""s are all positioned in plane or a plurality of planes.
The real scene may be a scene painted onto a background as used in theatres or may be an actual location.
The background scene may be any colour or combination of colours.
A plurality of television cameras may be positioned in front of the background scene, each camera being provided with a detecting device.
The present invention also provides a method of determining the position of a camera relative to a background, the method comprising the steps of:
positioning a plurality of LED""s in known fixed positions relative to the background, the LED""s forming an array;
detecting the positions of at least a proportion of the LED""s relative to the camera as the camera moves at each position of the camera; and
computing the position of the camera relative to the background.
Preferably the method further includes allocating to each LED in the array a specific code to thereby identify the LED and including the step of interrogating the output of each LED position to identify the code.
Preferably each array comprises at least seven LED""s. More preferably each array comprises between 10 and 30 LED""s but more or less could be used for more complex or very simple methods.
In a further embodiment the apparatus comprises a virtual reality system camera position system for a virtual studio, said system comprising a television camera providing a video output of a scene, an auxiliary detection device mounted on said television camera, a plurality of light emitting devices (LED""s) mounted in known fixed positions to form a defined array within said scene and including electronic detection means connected to said detection device, said detection means comprising position sensing analysis means for analysing the perspective of the defined array, as detected by said detector device, to provide a positional read out defining the position of said television camera relative to the LED array and comprising a virtual object store, a perspective transformation unit and a combiner unit in which the positional read out from the position sensing analysis means is connected to said perspective transformation unit to provide a transformation value, in which the virtual object store is connected to said combiner unit via said perspective transformation unit to transform the perspective and size of a virtual object to be inserted into said combiner unit and in which the video output of the scene provided by said TV camera is connected to said combiner circuit and in which the combiner circuit provides as an output a combined video image in which the virtual object is positioned in said scene.
The invention further provides a method for producing a combined video image comprising a real background scene viewed by a TV camera and a virtual reality foreground object, the method comprising the steps of;
positioning a plurality of LED""s in known fixed positions relative to the background scene, the LED""s forming an array,
detecting the positions of at least a proportion of the LED""s relative to the TV camera, as the camera moves, at each position of the camera, computing the position of the camera relative to the background,
selecting from a virtual reality store a virtual reality object to be positioned in the real background scene as viewed by the camera,
selecting the position for the virtual reality object in the scene,
transforming the size and perspective of the virtual reality object to conform to the calculated position of the camera relative to the background scene and combining the virtual reality object with the background scene to form a composite picture.